A UN report says cases of torture and mistreatment of detainees in Afghanistan have increased despite promises from President Ashraf Ghani and new laws enacted to curb the widespread practice.

At least 39 percent of the conflict-related detainees interviewed by UN investigators "gave credible and reliable accounts" of being tortured or experiencing other mistreatment at the hands of Afghan police, intelligence, or military personnel while in custody, the report says.

That compares with 35 percent of interviewees who reported such ill-treatment in the last UN report, released in 2015.

The Afghan government has acknowledged that problems could be caused by individuals but not as a national policy.

"The government of Afghanistan is committed to eliminating torture and ill-treatment," the government said in a statement.

The report by the UN Assistance Mission in Afghanistan (UNAMA) and the UN Human Rights Office (OHCHR) is based on interviews with 469 conflict-related detainees conducted over the past two years in 62 detention facilities administered by the National Directorate of Security (NDS), Afghan National Police, and other Afghan national-defense and security forces across the country.

"Torture does not enhance security," UN High Commissioner for Human Rights Zeid Ra'ad al-Hussein said in a statement. "Confessions produced as a result of torture are totally unreliable. People will say anything to stop the pain."

The UN report comes as senior Afghan officials prepare to appear before the UN Committee Against Torture in Geneva this week during a review of Afghanistan's record of implementing antitorture laws.

The International Criminal Court in The Hague is conducting a separate review of torture in Afghanistan.

"Notwithstanding the government's efforts to implement its national plan...the present report documents continued and consistent reports of torture and ill-treatment of conflict-related detainees, mainly during interrogation, and highlights a lack of accountability for such acts," UN officials concluded.

The document notes a 14 percent increase in reports of torture by Afghan National Police, at 45 percent of those interviewed.

The report says that more than a quarter of the 77 detainees who reported being tortured by the police were boys under the age of 18.

A force known as the Afghan Local Police severely beat almost 60 percent of their detainees, according to the interviews carried out by UN investigators.

Nearly 30 percent of interviewees held by Afghanistan's intelligence agency, the NDS, said they had faced torture or mistreatment.

Afghan National Army soldiers were also accused of mistreating some detainees.

Most detainees who reported being tortured said it was to elicit a confession, and the ill-treatment stopped once they signed a written confession. In many cases, they could not read the confession, the report says.

Torture methods included severe beatings to the body and soles of the feet with sticks, plastic pipes, or cables; electric shocks, including to the genitals; prolonged suspension by the arms; and suffocation.